The present invention relates to an improved method of connecting an end portion of a stator coil of a motor to a terminal as a metal piece for electrically connecting the stator coil to an external circuit.
There have been proposed some techniques in the prior art relating to a method of connecting a stator coil of a motor.
For example, Japanese Utility Model Laid-open Publication Nos. 60-7685, 60-144743, 60-144744 and 61-84655 disclose a method of connecting an end portion of a stator coil to a terminal by soldering. In such a connecting method by soldering, an operator is required to have a skill for soldering, and a working efficiency is accordingly low. Further, as a soldered portion is checked merely visually, a rejected product will be passed to a subsequent manufacturing step.
Referring to FIGS. 3 and 4 corresponding to another technique disclosed in Japanese Utility Model Laid-open Publication No. 62-125347, a pair of tabs 105 bent downwardly from a terminal 104 are press-fitted into a coil bobbin 114, and a pair of tabs 110 bent upwardly from the terminal 104 are employed for winding of an end portion of a stator coil 102 therearound. According to this method, it is necessary to take into consideration a thickness of the terminal 104, a wall thickness of the coil bobbin 114 is obliged to become large. Accordingly, a space in the coil bobbin 114 for winding the stator coil 102 is limited, causing a reduction in a degree of freedom of designing of the coil.
Referring next to FIGS. 5 and 6 corresponding to a further technique disclosed in Japanese Utility Model Laid-open Publication No. 62-185483, a lead wire 204 employed in substitution for the terminal is preliminarily connected to a stator coil 202, and a connecting portion 205 of the lead wire 204 and the stator coil 202 is inserted through a cable hole 203 to be led to a cable guide 230. Then, the connecting portion 205 is fixedly sandwiched between a holder 201 and the cable guide 230. According to this method, there is a possibility that the holder 201 will be loosened or removed because of vibration or the like of an automobile mounting the motor therein, for example.
Referring next to FIG. 7 corresponding to a still further technique disclosed in Japanese Utility Model Laid-open Publication No. 62-135578, reference numerals 322, 324 and 326 denote a welding source electrode, a first earth electrode and a second earth electrode, respectively. A welding current is supplied from the welding source electrode 322 to a connecting portion 310 between the terminal 304 and an end portion of a stator coil 302, so that heat due to contact resistance may be generated at the connecting portion 310. One end of the source electrode 322 is in contact with one end of the first earth electrode 324.
When the end portion of the stator coil 302 is placed on the terminal 304, a contact portion of the source electrode 322 and the first earth electrode 324 is pressed against the connecting portion 310 between the stator coil 302 and the terminal 304. The connecting portion 310 between the stator coil 302 and the terminal 304 is sandwiched under pressure between the second earth electrode 326 and the contact portion of the source electrode 322 and the first earth electrode 324. Under this condition, electric power is applied to the source electrode 322.
At the beginning of application of the electric power, a welding current is allowed to flow from the source electrode 322 directly to the first electrode 324 because the stator coil 302 is coated with an insulator. However, as a welding time proceeds, heat due to contact resistance between the source electrode 322 and the first earth electrode 324 is generated to melt and remove the insulator coated on the stator coil 302. As a result, all of the source electrode 322, the stator coil 302, the terminal 304 and the second earth electrode 326 are electrically conducted to allow the welding current to divisionally flow from the source electrode 322 through the stator coil 302 and the terminal 304 to the second earth electrode 326. There is also generated heat due to contact resistance between the stator coil 302 and the terminal 304 by the welding current. Then, the terminal 304 is welded to the stator coil 302, thus completing connection between the stator coil 302 and the terminal 304 in several seconds from the beginning of application of the electric power.
In this case, a heat quantity generating at the welding portion is a function of the contact resistance and the welding current. Accordingly, optimum control of welding can be effected by suitably controlling the welding current, thus ensuring the connection. Further, even when a rejected product is manufactured, the determination of rejection can be made easily. Thus, this technique has solved the problems in the previous techniques as shown in FIGS. 3 to 6.
However, in the technique as shown in FIG. 7, the end portion of the stator coil 302 and the terminal 304 under the overlapped condition are sandwiched under pressure between the upper electrodes 322 and 324 and the lower electrode 326. Therefore, it is necessary to define a space for inserting the second earth electrode 326 in the inside of the stator. As a result, another space for mounting a coil bobbin and the other parts in the stator is limited, and accordingly the size of these parts must be made small to cause a reduction in a degree of freedom of designing.
To solve this problem, if all the terminals are so positioned as to press the end portion of the stator coil and the terminal in one direction from the outside of the stator, there will occur another problem that the terminal will be deformed.